A 10-year-old child with sho stature presented to the pediatric OPD with external ophthalmoplegia, gait abnormality, sensorineural hearing loss. Lab findings revealed raised fasting blood glucose levels. ECG Fundus examination Which of the following is true about the DNA involved in the above disease: –
## **Core Concept**
The question describes a child with short stature, external ophthalmoplegia, gait abnormality, sensorineural hearing loss, raised fasting blood glucose levels, and unspecified ECG and fundus examination findings. This combination of symptoms suggests a mitochondrial disorder, specifically **Kearns-Sayre Syndrome (KSS)** or a similar condition like **Mitochondrial Encephalomyopathy, Lactic Acidosis, and Stroke-like episodes (MELAS)**. However, the specific constellation of symptoms and lab findings points more towards a disorder related to mitochondrial DNA.
## **Why the Correct Answer is Right**
The symptoms described—short stature, external ophthalmoplegia, gait abnormality, sensorineural hearing loss, and raised fasting blood glucose levels—are indicative of a systemic condition affecting multiple body systems. **Mitochondrial DNA (mtDNA) mutations** are known to cause a variety of disorders because mitochondria are present in nearly all cells and play critical roles in energy production. Kearns-Sayre Syndrome, for example, is characterized by external ophthalmoplegia, pigmentary retinopathy (which could be part of the unspecified fundus findings), and often, elevated blood glucose levels. Mitochondrial disorders are inherited solely from mothers, as only egg cells contribute mitochondria to the zygote. The correct answer involves understanding that mitochondrial DNA diseases are due to mutations in the mtDNA, which is inherited maternally.
## **Why Each Wrong Option is Incorrect**
- **Option A:** This option might suggest a nuclear DNA involvement. While many mitochondrial proteins are encoded by nuclear DNA, the inheritance pattern and the specific symptoms described point towards a mitochondrial DNA issue rather than a purely nuclear one.
- **Option B:** This could imply a specific type of inheritance or genetic mechanism not directly related to mitochondrial function or could be a distractor related to another genetic condition.
- **Option C:** Similarly, this might imply another genetic mechanism or condition not directly related to the symptoms described.
## **Clinical Pearl / High-Yield Fact**
A key point to remember is that **mitochondrial DNA diseases** are **solely maternally inherited** because only egg cells contribute mitochondria to the fertilized egg. This is a critical distinguishing feature from diseases caused by mutations in nuclear DNA. Conditions like Kearns-Sayre Syndrome and MELAS syndrome highlight the importance of considering mitochondrial function in patients with multisystemic symptoms.
## **Correct Answer:** .